Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/10—Printing inks based on artificial resins
  • C09D11/101—Inks specially adapted for printing processes involving curing by wave energy or particle radiation, e.g. with UV-curing following the printing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M3/00—Printing processes to produce particular kinds of printed work, e.g. patterns
  • B41M3/14—Security printing
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D11/00—Inks
  • C09D11/02—Printing inks
  • C09D11/10—Printing inks based on artificial resins

Definitions

• This invention belongs to the field of printing inks. More specifically, it is related to printing inks which are capable of being polymerized by cationic initiation and which are to be used in the method of engraved steel die printing, especially for the printing of security documents such as checks, shares, airline tickets, banknotes, etc.
• intaglio printing comprises the use of printing ink carrying surfaces, typically printing cylinders or printing plates, where the pattern to be printed is engraved and the engravings are filled with printing ink to be transferred to the printing substrate in order to create the document.
• intaglio printing shall only mean the so-called "engraved steel die printing process” where chromium plated, engraved steel or nickel plates or cylinders are used, and shall not include the well known rotogravure or gravure printing processes.
• this invention does not relate to very low viscous printing inks for the conventional gravure printing where a totally different concept of ink formulation is necessary. It is rather related to printing inks having a honey-like or even pasty viscosity for engraved steel die printing.
• a rotating engraved steel cylinder where the pattern or image to be printed is engraved, is supplied with ink by one or more template inking cylinders by which a pattern of inks of different colour is transferred to the printing cylinder.
• Any excess of ink on the plain surface of the printing cylinder is wiped off by a rotating wiper cylinder covered by a plastisol, using diluted aqueous sodium hydroxide as an emulsifying medium for the wiped-off excess ink, or a paper/calico wiping device, or, otherwise, trichloroethylene.
• the printing pattern in the engravings of the printing cylinder is transferred, under a pressure up to about 500 bars, on the substrate to be printed which may be paper or plastic material in sheet or web form.
• the engravings of the printing cylinder have a depth comprised between about 30 and 200 micrometers or even more (whereas rotogravure cylinder engravings are only about 2 to 20 micrometers deep), and the ink transferred to the printed substrate gives a thick and generally strongly pigmented film.
• Film forming characteristics allowing further manipulation of sheets or webs carrying printed films of up to 200 microns thickness 24 hours after printing or respectively immediately after printing.
• Non-offseting properties In case of web printing at speeds up to 150 m/min, the immediate rewinding of the printed substrate is mandatory. The ink system has to assure that there is no transfer from the printed surface to the substrate in contact therewith.
• the printed substrates must be dried in order to allow subsequent processing and to achieve the required properties of the final product.
• drying two different mechanisms are comprised.
• the mere physical drying means the evaporation of ink solvents whereas chemical drying, also called hardening or curing, means the transition of a composition from a liquid state into the solid state by polymerization or crosslinking.
• chemical drying also called hardening or curing, means the transition of a composition from a liquid state into the solid state by polymerization or crosslinking.
• the printer does generally not make any difference between physical and chemical drying.
• heat set process uses heat supplied directly by gas burners or infrared lamps, or externally heated air which is directed to the printed sheets. This brings about an accelerated physical and also chemical drying and the possibility to introduce continuous web printing.
• heat set processes have the following serious drawbacks:
• drying speed is insufficient.
• Another method for rapidly drying an ink is the use of radiant energy, namely, accelerated electrons supplied by electron cannons (electron beam process), and ultra-violet (UV) radiation,
• Electron beam curing or drying apparatuses are most expensive.
• electron beam radiation may have a detrimental effect on the mechanical properties of printing substrates.
• the drying by UV radiation has been widely introduced into the printing art.
• the drying is initiated by radicals, created by the UV radiation, but different from radical formation in electron beam methods. Since the energy of UV rays is low compared with electron beams, the direct scission of radical forming molecules is impossible. Therefore, it is necessary to incorporate a photoinitiator into the printing ink which is decomposed on the impingement of a UV irradiation and will form the free radicals necessary for curing. In this manner, it is virtually impossible to dry or cure the thick and strongly pigmented ink layer obtained in engraved steel die printing.
• the reasons therefor are the following:
• pigments and extenders may further inhibit free radical polymerization
• the ambient oxygen also inhibits the drying through termination reactions
• Still another object of the invention is to provide such printing inks which will allow the engraved steel die printing of security documents on both faces of a printing substrate in web or sheet form in one passage on the same press.
• a further object of the invention is to provide such printing inks which employ another mechanism of curing than the already known engraved steel die printing inks and which bring about new and unforeseen advantages and cancels the disadvantages of the drying of known inks.
• a further object of the invention is to provide printing inks as defined above which can be cured by sensible or radiating heat, by other energy radiations such as electron beam or UV, or by a combination of radiative and non-radiative energy.
• Still another object of this invention is to provide new engraved steel die printing inks of the above indicated kind which allow a perfect and easy wiping of the printing cylinder with the use of water, of diluted sodium hydroxide solutions or trichloroethylene, as well as according to the paper/calico method.
• the inks of this invention thus contain such photoinitiators capable of liberating a Lewis acid or a Bronsted acid on activation by energy.
• photoinitiators capable of liberating a Lewis acid or a Bronsted acid on activation by energy.
• these photoinitiators have already been proposed for printing inks, the person skilled in the art could not think of using them in engraved steel die printing inks since the monomers or prepolymers which can be polymerized by cationic initiators are generally of low viscosity, and engraved steel printing inks are of pasty consistence and have to fulfill particular requirements as already pointed out above.
• the inventors have found that the printings obtained with the engraved steel die printing inks of the invention can also be cured by heat or a combination of heat and UV radiation readily available on existing machinery for security documents printing. This will be described in detail later on.
• the ink of the invention basically contains four groups of components.
• Group A comprises the organic binder matrix.
• the organic binder contains at least one compound which is capable of being polymerized by a cationic reaction mechanism an activation of a photoinitiator.
• the organic binder should also impart to the ink system the required rheology for engraved steel die printing.
• the amount of Group A components generally comprises between about 20 and about 60% by weight of the ink.
• Group B comprises at least one onium salt based curing initiator.
• the amount of Group B components generally comprises between about 1 and about 15% by weight of the ink.
• Group C comprises inorganic and/or organic pigments, fillers and extenders.
• the amount of Group C components may be up to about 60% by weight of the ink.
• Group D comprises different additives such as stabilizers, emulgators, dispersing agents, waxes, plasticizers, viscosity and rheology regulators and diluents.
• the amount of Group D components is comprised between 0 and about 20% by weight of the ink.
• the components of the ink are selected such that the cone plate viscosity (shear rate about 1000 s -1 ) at 40° C. is equal to or higher than 1 Pa ⁇ s.
• Group A basically contains at least one cationically polymerizable material. This term refers to all compounds which contain cationically polymerizable moieties and which can be generally described as follows:
• oxirane group containing materials butyl glycidyl ether, butanediol glycidyl ether, C 12 -C 14 alkyl glycidyl ether, cresyl glycidyl ether, isooctyl glycidyl ether, 1, 6-hexanediol glycidyl ether, bisphenol A ethoxylate diglycidyl ether, glyceryl propoxylate triglycidyl ether, neopentylglycol propoxylate diglycidyl ether, trimethylolpropane ethoxylate triglycidyl ether, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 1,2-epoxy-p-vinylcyclohexene, bis(3,4-epoxycyclohexyl)adipate, vinylcyclohex
• vinyl compounds diethyleneglycol divinyl ether, triethyleneglycol divinyl ether, cyclohexanedimethanol divinyl ether, hydroxybutyl vinyl ether, dipropyleneglycol divinyl ether, tripropyleneglycol divinyl ether, and aliphatic, aralkyl, arylalkoxy mono and divinyl ethers.
• none of the aforementioned reactive compounds is capable of bringing about the adequate rheology for engraved steel die printing inks.
• thermoplastic materials such as cellulose derivatives, homopolymers or copolymers of acrylics and vinylics, oil free polyesters, polyacetals, polyurethanes and other high viscous polymeric materials in the cationically polymerizable compounds listed above allows to achieve the required rheology without impairing the drying capacity of the system.
• the polymerizable binder material can be selected from cationically polymerizable monomeric, oligomeric and polymeric unsaturated organic compounds, and hereocyclic compounds capable of undergoing a ring-opening reaction and their mixtures, said compounds having been chain extended in order to raise molecular weight and viscosity.
• modification of polyfunctional epoxy derivatives with di or polyfunctional carboxylic acids allows one to impart to the binder matrix A the required rheology while maintaining a sufficient degree of cationic reactivity.
• binder matrix A Another possibility to achieve the required viscosity and molecular weight of the binder matrix A is the polyaddition reaction of one or more hydroxy groups containing vinyl ethers on di or polyisocyanates. Such compounds as well as methods to obtain them are disclosed in U.S. Pat. No. 4,751,273 (Lapin et al) which is incorporated in this specification by reference.
• Group B components comprise at least one energy sensitive onium salt capable of liberating a cationic polymerization initiator or catalyst under the influence of applied energy.
• Particularly preferred are salts of the formula Ar 3 S + X - wherein Ar is a monovalent aromatic radical, S is sulfur, and X - is [MF 6 ] - wherein M is P, As or Sb.
• the compounds of group B are generally known per se. In the prior art, they are termed as radiation sensitive initiators, see U.S. Pat. No. 4,138,255 and EP-A2-0 334 056 (both to Crivello) incorporated in this description by reference. This means to the person skilled in the art that they can be activated by UV light or electron beams. They can also be activated by the application of thermal energy, namely hot fluids such as hot air of about 120° to 280° C. or infrared waves. Surprisingly, it has been found that the energy sensitive initiators used in this invention, are appropriate to cure or dry highly pigmented or charged inks.
• the Crivello references do not disclose the presence of inert components in the curable mixtures it could not be expected that highly filled inks containing up to 60% by weight of inert materials would cure in a relatively short time.
• Group C components are generally not different from those currently used in intaglio printing inks. Any organic and inorganic pigment appropriate for printing inks may be used; these colour pigments are well known to the man skilled in the art and need not be described in detail. The same applies to the extenders or fillers; examples thereof are calcium carbonate, barium sulfate and titanium dioxide.
• Group D components are also those which are currently used in engraved steel die printing inks; they comprise, for example, stabilizers to assure a predetermined pot-life of the ink, emulsifiers and dispersing agents for the pigments and the extenders, plasticizers for the regulation of the flexibility of the final film, cationically polymerizable and/or non-reactive diluents for adjusting flow and transfer characteristics of the ink, and others.
• Curing is accomplished throughout the whole mass of the printed marks and is not confined to surface regions.
• Curing proceeds rapidly throughout the mass of the printed marks even after removing the energy source ("dark cure").
• Curing is accomplished on the application of heat, UV rays, electron beams and other irradiations including IR.
• Curing is not oxygen inhibited, and nitrogen blanketing is no longer necessary.
• the initiators have a perfectly satisfactory stability as to time (shelf life) and also to moderately elevated temperatures.
• Curing is accomplished with a minimum of volume change which assures good adhesion properties of the printed ink film.
• UV irradiation is the preferred curing method for the inks of the invention.
• UV curing has effectively numerous advantages on other curing or drying methods: Low capital requirement for UV sources and devices, enhanced curing speed due to the IR portion of the irradiation no negative influence on the mechanical properties of security document paper, etc.
• the inks of this invention may be blended with other engraved steel die printing inks capable of curing by other reaction mechanisms, known in the art, such as oxypolymerization, UV or electron beam induced free radical polymerization, or others.
• Synthesis of a cationically polymerizable binder varnish 96 parts of a cycloaliphatic epoxide (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate solid as CYRACURE UVR 6110--Union Carbide) are heated in the appropriate vessel under nitrogen at 130° C. 4 parts of fumaric acid acid are added and allowed to react for about 2 hours, while the temperature is raised to 150°-155° C. The final acid number of the reaction product is 0.2 mg KOH/g and the varnish has a viscosity of 18 Pa ⁇ s at 40° C.
• a UV cationically polymerizable printing ink is manufactured by classical means (e.g. mixing of all ingredients, then grinding on 3 roller-mills) according to the following formula:
• the ink has a viscosity of 12.5 Pa ⁇ s at 40° C. It shows an excellent response to cure with UV light, as well as a very good dark cure.
• the ink is paper wipeable and fulfills all the requirements needed by engraved steel die inks to be used for printing of security documents,
• 88 parts of a cycloaliphatic epoxide (CYRACURE UVR 6110--Union Carbide) are heated under nitrogen at 100° C. in appropriate vessel. 12 parts of a polyvinyl butyral resin (MOWITAL B60-M--Hoechst) are then portionwise introduced while agitating vigorously until complete dissolution is achieved. Final viscosity is 13 Pa ⁇ s at 40° C.
• a UV cationically polymerizable ink is manufactured by classical means, according to the following formula:
• micronized polyethylene wax CERIDUST 9615A--Hoechst
• surfactant STYRENE L 7604--Union Carbide
• the ink has a viscosity of 14 Pa ⁇ s at 40° C. It is paper wipeable and shows the same excellent properties as the ink described in example I.
• the new inks of the invention are used in the same manner as the inks known before. They are valuable compositions for the printing of security documents, such as banknotes, checks, traveller checks, credit cards, stamps, shares, passports, airline tickets, labels and similar documents for which measures against counterfeiting and forgery are necessary or indicated.
• security documents such as banknotes, checks, traveller checks, credit cards, stamps, shares, passports, airline tickets, labels and similar documents for which measures against counterfeiting and forgery are necessary or indicated.

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• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Wood Science & Technology (AREA)
• Organic Chemistry (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)
• Macromonomer-Based Addition Polymer (AREA)

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Citations (14)

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• 1990
  • 1990-11-19 AT AT90810883T patent/ATE128478T1/de not_active IP Right Cessation
  • 1990-11-19 EP EP90810883A patent/EP0432093B1/fr not_active Expired - Lifetime
  • 1990-11-19 DK DK90810883.0T patent/DK0432093T3/da active
  • 1990-11-19 DE DE69022694T patent/DE69022694T2/de not_active Expired - Lifetime
  • 1990-11-19 ES ES90810883T patent/ES2077664T3/es not_active Expired - Lifetime
  • 1990-11-22 AU AU66897/90A patent/AU635583B2/en not_active Expired
  • 1990-11-26 ZA ZA909487A patent/ZA909487B/xx unknown
  • 1990-11-29 CA CA002031146A patent/CA2031146C/fr not_active Expired - Lifetime
  • 1990-11-30 JP JP2336996A patent/JP2966922B2/ja not_active Expired - Lifetime
• 1995
  • 1995-06-06 US US08/466,345 patent/US5658964A/en not_active Expired - Lifetime
  • 1995-09-28 GR GR950402261T patent/GR3017540T3/el unknown

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